Vibration isolation systems are known. For example, EP 927 380 B1 discloses a vibration isolation system having air bearings, which is used in particular as the bearing for a lithography appliance. The disclosure content of this Laid Open Specification is hereby made the subject matter of the application.
Vibration isolation systems such as these are used in many other areas of technology. Particularly in the semiconductor industry, the requirements for the vibration isolation system on which, for example, manufactured installations are mounted are becoming more stringent as miniaturization progresses further.
Vibration isolation systems having air bearings may have an active control system in which one or more position sensors detect the position of the load to be mounted, with the compressed-air supply to the air bearings being controlled on the basis of the position detection. If the vibration isolation system is loaded with a relatively heavy load, active control such as this automatically increases the air pressure, thus providing level compensation.
The control loop which provides this level compensation is relatively slow because of the pneumatic valves, which respond relatively slowly, and because of the large volume of air in the system, generally achieving a control bandwidth of less than 3 Hz. High-frequency vibration therefore cannot effectively be counteracted by this control loop. In fact, only level compensation is essentially feasible.
In order to make it possible to reduce more rapid position changes, for example caused by vibration resulting from resonances, vibration isolation systems exist which, in addition to control of the compressed-air supply, have actuators which act on the load to be isolated without contact, and are operated via a further control loop.
For actuators such as these, which may be in the form of magnetic actuators or piezo-actuators, the corresponding control loops achieve control bandwidths with frequencies of more than 200 Hz. One disadvantage that has been found is that these actuators draw a large amount of current and, since they operate independently of the pneumatic control, frequently counteract the pneumatic control.